1. Field of the Invention
This invention relates to a pickup for recording or reproducing data with respect to a disk recording medium, and more particularly to a traveling speed detection device for deriving a speed signal precisely corresponding to the traveling speed thereof.
2. Description of the Related Art
As is well known in the art, in the field of audio instruments and video instruments, digital recording/reproducing systems for converting an information signal such as an audio signal or video signal into digital data, recording the digital data on a recording medium such as a magnetic tape or disk and reproducing the recording medium to derive an original information signal have been widely used. Among the above systems using a disk as a recording medium, for example, an optical reproducing device such as a CD (compact disk) player or VD (video disk) player is now dominantly used. Recently, a data re-programmable optical disk called an additionally recording type optical disk has been put into practice, and optical disk recording/reproducing devices for recording and reproducing data with respect to the additionally recording type optical disks as well as the above-described optical disk reproducing devices have been actively developed.
An optical pickup for recording or reproducing data with respect to the above-described optical disk has a pickup lens which is suspended by means of a wire spring so as to be moved in a tracking direction and focusing direction. Therefore, when external force is applied thereto, the pickup lends tends to vibrate at a fixed frequency of fo determined by it and the wire spring and the amplitude of the vibration is large so that it will take a long time for the vibration to be sufficiently attenuated. This problem is explained by taking, as an example, a so-called search operation in which desired data is searched by moving the pickup in the radial direction of the disk at a high speed.
That is, as shown in FIG. 1(A), when a search control signal is changed from an "L" (low) level to an "H" (high) level to start the search operation, a tracking servo control signal is changed from the "H" level to the "L" level as shown in FIG. 1(B) to set the tracking servo from the ON state to the OFF state, rotate a pickup feeding motor at a high speed and move the pickup in the radial direction of the disk at a high speed. At this time, as shown in FIG. 1(C), the pickup lens vibrates at a fixed period (1/fo), and as shown in FIG. 1(D), the envelope component of the tracking error signal is set at the constant level.
When pulses of a number corresponding to the rotation number of the pickup feeding motor is counted and it is determined that the pickup has reached a target position, then the search control signal is changed from the "H" level to the "L" level to interrupt the rotation of the motor and movement of the pickup. However, even when the movement of the pickup is interrupted, vibration of the pickup lens is not sufficiently attenuated as shown in FIG. 1(C). While the pickup lens is being vibrated, it is impossible to stably set the pickup lens even after the tracking servo is set into the ON state.
Therefore, it is necessary to set the tracking servo into the ON state by inverting the tracking servo control signal from the "L" level to the "H" level after time t from the time the movement of the pickup is interrupted until the vibration of the pickup is naturally attenuated has elapsed. For this reason, a period from the time the movement of the pickup is interrupted until the tracking servo is set into the ON state for the reproducing operation becomes longer because of the presence of wait time t and it takes a long time to effect the search operation.
In order to reduce the search time by setting the wait time t as short as possible, it has been proposed to use means for forcedly stopping the vibration by conducting current in a tracking actuator coil for driving the pickup lens in the tracking direction to move the pickup lens in a direction opposite to the vibration direction or means for detecting the speed component of the pickup lens based on an output of a sensor mounted for detecting the relative movement between the pickup and the pickup lens and feeding back the detection result to the tracking actuator coil.
However, when the former means is used, it is difficult to determine the direction and magnitude of the vibration of the pickup lens, and therefore, the pickup lens may be made to vibrate to a larger extent and it is impossible to suppress the vibration when the pickup is vibrated by externally applied impact. Further, when the latter means is used, the sensor is used, and therefore, the construction of the pickup becomes complicated, large and economically disadvantageous.